Lit. “prohibited.” That which is unlawful. The word is used in both a good and a bad sense e.g. Baitu ‘l-haram, the sacred house; and Malu ‘l-haram, unlawful possessions. Ibnu ‘l-haram, an illegitimate son; Shahru ‘l-haram a sacred month.
A thing is said to be haram when it is forbidden, as opposed to that which is halal, or lawful. A pilgrim is said to be haram as soon as he puts on the pilgrim’s garb.
Haramu ‘llah la afa’lu is a form of oath that a man will not do a thing.
Based on Hughes, Dictionary of Islam